Dexterous robots are able to precisely grasp and manipulate objects using a series of linkages, which in turn are interconnected via one or more motor-driven robotic joints. End-effectors are the particular linkages used to perform a given task at hand, such as grasping and maneuvering a work tool or other object. Humanoid robots are a particular type of dexterous robot having an approximately human structure, e.g., a full body, torso, hand(s), and/or another appendage(s). The structural and control complexity of any robotic system is largely dependent upon commanded work tasks, and therefore dexterous robots present a substantially greater control challenge relative to the control of conventional robots.
Dexterous robots may include one or more end effectors, such as a robotic wrist assembly having an open wrist joint, the proper control of which can enable a more precise handling of a grasped object. An open wrist joint results in wrist degrees of freedom that are actuated by indirect drives in a closed-chain mechanism. The mapping between the actuator space of any velocity-controlled wrist actuators and the joint space itself is thus coupled and nonlinear, as is understood in the art. Therefore, such a wrist joint can end up having an irregularly-shaped permissible workspace. Stable operation of a robotic mechanism operating within such a workspace is paramount to the optimal functioning of the robotic system.